1. Field of the Invention
The present invention relates to a function of automatically centering object images in image pickup apparatuses such as video cameras, electronic endscopes, etc.
2. Description of the Related Art
Small-sized, lightweight image pickup apparatuses, such as endscopes, have been widely used for medical and industrial purposes. FIG. 8 is a schematic illustration of a conventional endscope, which includes a scope 11 which is adapted to be inserted into a narrow cavity within a human body and take in reflected light from a deceased part of the body to be examined, a camera head 14 containing a prism 13 and an imaging devices 3, and an adapter 12 for coupling the scope 11 with the camera head. Note that the prism 13 is used only when three imaging devices for three primary colors are used (i.e., three-plate type).
With conventional endscopes, the registration of a circular image obtained through the scope 11 with the center of the display screen has been achieved by using high-precision parts for mounting structures and regulating adjustable parts so that the scope 11, the adapter 12, the prism 12 and the imaging devices 3 are optically aligned with one another.
Thus, the conventional endscopes entail high manufacturing costs because of the use of high-precision parts and regulation work requirements of adjustable parts. When the scope or adapter is replaced, the object image may become offset from the center (a desired position) of the display screen due to variations in the scope or adapter. In that event, the adjustable parts must be regulated again.
For instance, Japanese Patent Application KOKAI Publication No. 2001-46331 discloses a technique in which, if, in displaying an endscope image with enlargement, the image is displaced through operation of an enlargement knob, the curved portion of the end of the scope is curved according to a displacement of the image, thereby compensating for the displacement. However, this patent publication does not disclose any compensation method when the image is displaced from the desired position on the display screen.